The present invention relates to a plasma process device for applying various plasma processes, such as an etching process, to a substrate.
Up until now, when a substrate is processed by etching, sputtering, or CVD in semiconductor manufacturing processes, a plasma process device has been used. In the plasma process device, a predetermined process is applied to a substrate such as a semiconductor wafer (hereinafter, referred to as "wafer") in a plasma atmosphere which is generated by introducing a process gas into a process vessel and converting the process gas into a plasma-state gas. In recent years, the degree of integration of semiconductor devices has been increased and wafers have become larger. Under these circumstances, it is considered particularly important that a micro process is performed uniformly at a high rate in the plasma process device.
Taking an etching device for example, it is desirable to attain the micro-processing by generating a high density plasma in a process chamber. Simultaneously it is also desirable that etching be performed uniformly over the entire wafer at a higher rate.
To attain these, a plasma generation device having a dipole ring magnet is proposed by Jpn. Pat. Appln. KOKAI Publication No.6-53177. The dipole ring magnet is formed of a plurality of anisotropic segment magnets arranged along the outer periphery of a process vessel. This plasma generation device is developed to attain more uniform plasma density than in a conventional device using a magnetron plasma, by improving the uniformity of a magnetic field, particularly the uniformity of the magnetic field along the surface of a substrate.
In the conventional dipole ring magnet formed of the anisotropic segment magnets, the intensity distribution of the resultant magnetic field on or above the substrate, formed by the dipole ring magnet exhibits virtually an oval shape, as shown in FIGS. 11A and 11B. The N-S pole direction corresponds to the short axis of the oval. The perpendicular direction (E-W pole direction) to the N-S pole direction corresponds to the long axis of the oval. Because of the oval shape, the intensity of the magnetic field of the N-S pole direction differs from that of the perpendicular direction. As a result, the magnetic field cannot be formed uniformly over the entire surface of the substrate with a high accuracy. In FIG. 11A, the abscissa indicates a horizontal distance from a center of a substrate. The ordinate indicates an intensity of the magnetic field. Curve a represents an intensity distribution of the magnetic field in the N-S pole direction. Curve b represents an intensity distribution of the magnetic field in the E-W pole direction. FIG. 11B shows a magnetic-field distribution parallel to the upper surface of a substrate. The abscissa indicates the N-S direction. The ordinate indicates the E-W pole direction. The intersection between the ordinate and the abscissa coincides with the center of the substrate surface. Considering an influence of an E.times.B drift movement of the electrons in a plasma, the electrons tend to move to the side of the W-pole from the side of the E-pole side, so that the electrons are collected on the W-pole side. To prevent this influence, it is necessary to form a so-called inclined magnetic field in which the intensity of the magnetic field decreases toward the W-pole side from the E-pole side to change the drift movement direction of the electrons so that the electrons are not collected on one pole side. It is preferable to perform a uniform plasma process such that the anisotropic segment magnets constituting the dipole ring form a magnetic field parallel to the processing surface of the wafer over the wafer in the plasma area. However, in practice, the generated magnetic field have upwardly and downwardly projected curve components on the upper and down sides. Therefore, it is difficult to further improve the uniformity of the plasma density. This is a reason why the plasma process is not performed uniformly.